Using a vector generated in SAS/IML as a macro variable

Question

I am writing a macro that will run PROC MIXED with the level-1 residual variance fixed to a near-zero value using the PARMS statement. I am trying to generate the bulk of the starting values for the PARMS statement using SAS/IML, something like:

%macro test (dataset= , classroom= , preds= , outcome=);
proc iml;

/*count number of variables*/
    %let nvars = 0; 
    %do %while(%qscan(&preds,&nvars+1,%str( )) ne %str());
        %let nvars = %eval(&nvars+1);
    %end; 

/*determine location of level-1 residual in the start value vector*/
    %let error_location = %eval(((&nvars*(&nvars-1))/2)+&nvars+1);

/*create vector of start values from lower triangle of identity matrix*/
    start_vector = symsqr(I(&nvars));
    %let starts = %str(start_vector[label=""]); 

/*analyze data*/
    proc mixed data=&dataset noprofile method=ml;
        class &classroom;
        model &outcome = &preds /noint;
        random &preds /type=un sub=&classroom g; 
        parms 
            &starts
            .00000001 /hold= &error_location;
    run;
quit;
%mend;

The code works fine without the PARMS statement in the PROC MIXED code. When I run the code as is, however, SAS apparently puts the literal string 'start_vector[label=""]' after PARMS rather than listing the values generated by IML.

How can I avoid this error and have SAS specify the values contained in START_VECTOR as starting values for the PARMS statement?

Answer 1

You should use the SYMPUT or SYMPUTX routines in SAS/IML to convert a vector to a macro variable.

This is one way to get a vector into a single string in a macro variable.

proc iml;
  start = {"Hi","Bye"};
  call symput("start",rowcat(start`));
  %put &start;
quit;

With a numeric vector, you need to use char to convert it:

proc iml; start_vector = j(5); call symputx("start_vector",rowcat(char(j))); %put &start_vector; quit;

With a numeric matrix, you need to use SHAPE to flatten it:

proc iml; 
    start_vector = j(5,5); 
    call symputx("start_vector",rowcat(shape(char(start_vector),1))); 
    %put &start_vector;
quit;